1) Field of the Disclosure
The disclosure relates generally to fibers with nanostructure reinforcement, and more particularly, to core-sheath carbon fibers with core nanostructure reinforcement and gradient properties for use in composite structures for aircraft and other structures.
2) Description of Related Art
Fiber-reinforced resin materials, or “composite” materials as they are commonly known, are used in a wide variety of structures and component parts, including in the manufacture of aircraft, spacecraft, rotorcraft, watercraft, automobiles, trucks, and other vehicles, because of high strength-to-weight ratios, corrosion resistance, and other favorable properties. In particular, in aircraft construction, composite structures and component parts are used in increasing quantities to form the fuselage, wings, tail section, skin panels, and other component parts of the aircraft.
Conventional composite materials typically include glass, carbon, or polyaramid fiber “plies” in woven and/or non-woven configurations. The fiber plies can be manufactured into composite parts by laminating them together with an uncured matrix material (e.g., an epoxy resin). The laminate can then be cured with the application of heat and/or pressure to form the finished part.
The fiber material in composite parts provides relatively high strength in the direction of the fibers. Impact resistance, however, is generally determined by the properties of the cured matrix. Carbon fibers with high moduli and strengths may have issues at the fiber-matrix interface when there is a mismatch between the stiffness of the matrix and the fiber. Known composite materials exist with higher moduli and strengths than currently used high-to-intermediate-modulus fibers. However, such known composite materials have shown a susceptibility to decreased interface properties between the fiber and matrix, thus limiting the benefits available from such higher-performance fibers. In addition, known methods exist that either modify the fiber sizing or use different matrix chemistries. However, such known methods may not overcome the susceptibility to decreased interface properties between the fiber and matrix while still providing improved fiber properties. Moreover, such known methods may increase the weight of the composite materials and may increase costs of manufacturing and production of the composite materials.
Further, another way to increase the impact resistance and fracture toughness of composite parts is to enhance the structural properties of the composite materials by adding nanostructures, such as carbon nanostructures, to the composite materials. Carbon nanotubes are ordered molecules of pure carbon which form very small cylinders (on the order of 10 nanometers (i.e., 1×10−8 meters)). Carbon nanotubes exhibit unusual strength, and may be over 30 times as strong as typical carbon fibers and 100 times stronger than steel of equivalent weight.
Known composite materials having nanostructure reinforcement, such as carbon nanotube reinforcement, exist. However, such known composite materials may suspend the carbon nanotubes in resin resulting in random orientation of the nanotubes between adjacent fiber plies. Moreover, the addition of even small amounts of carbon nanotubes to a liquid resin tends to dramatically increase its viscosity and, thus, decrease its processability. Further, conventionally produced carbon fibers typically used in aerospace composite materials and other composite materials may have amorphous microstructures in the core of the fiber and ordered, graphitic structures in the outer portion of the fiber, which may result in substantial strength and stiffness from such fibers being derived from the outer portion of the fiber.
Accordingly, there is a need in the art for an improved fiber with more-tailorable properties for use in composite materials and a method of making the same that provide advantages over known materials and methods.